Heart sounds template comparison to identify true pacing mode

ABSTRACT

An apparatus may include an implantable therapy circuit that provides bi-ventricular pacing to a subject, a heart sound signal sensing circuit that produces a sensed heart sound signal that is representative of at least one heart sound associated with mechanical cardiac activity, a memory circuit to store one or more heart sound templates of cardiac capture, and a comparison circuit that compares a segment of the sensed heart sound signal to the one or more heart sound templates of cardiac capture to identify ventricles in which cardiac capture was induced by the bi-ventricular pacing. In some situations, an indication of the ventricles in which cardiac capture was induced may be generated according to the comparison.

CLAIM OF PRIORITY

This application is a continuation of U.S. application Ser. No.14/187,954, filed Feb. 24 2014, now issued as U.S. Pat. No. 9,320,906,which claims the benefit of U.S. Provisional Patent Application Ser. No.61/776,941, filed on Mar. 12, 2013, the benefit of priority of each ofwhich is claimed hereby, and each of which is incorporated by referenceherein in its entirety.

BACKGROUND

Ambulatory medical devices include implantable medical devices (IMDs)and wearable medical devices. Some examples of IMDs include cardiacfunction management (CFM) devices such as implantable pacemakers,implantable cardioverter defibrillators (ICDs), cardiacresynchronization therapy devices (CRTs), and devices that include acombination of such capabilities. The devices can be used to treatpatients or subjects using electrical or other therapy, or to aid aphysician or caregiver in patient diagnosis through internal monitoringof a patient's condition. The devices may include one or more electrodesin communication with one or more sense amplifiers to monitor electricalheart activity within a patient, and often include one or more sensorsto monitor one or more other internal patient parameters. The devicesmay be implanted subcutaneously and include electrodes that are able tosense cardiac signals without being in direct contact with the patient'sheart. Other examples of IMDs include implantable diagnostic devices,implantable drug delivery systems, or implantable devices with neuralstimulation capability.

Some examples of wearable medical devices include wearable cardioverterdefibrillators (WCDs) and wearable diagnostic devices (e.g., anambulatory monitoring vest). WCDs can be monitoring devices that includesurface electrodes. The surface electrodes are arranged to provide oneor both of monitoring to provide surface electrocardiograms (ECGs) anddelivering cardioverter and defibrillator shock therapy.

In response to an abnormally slow heart rate or lack of coordinationamong contraction of the ventricles, some CFM devices deliver electricalpacing stimulation to induce cardiac depolarization and contraction(sometimes referred to as capture of the heart). It is desirable for aphysician to know the effectiveness of the pacing stimulation therapyprovided to the subject. A system and method for monitoring at least onechamber of a heart during delivery of refractory period stimulation todetermine if desired non-capture occurs can be found in Chinchoy et al.,“Mechanical Ventricular Pacing Non-Capture Detection for a RefractoryPeriod Stimulation (RPS) Pacing Therapy Using at Least One Lead-BasedAccelerometer,” U.S. Patent Application Publication No. US 2008/0269825,filed Apr. 30, 2007. An implantable cardiac rhythm management devicecapable of automatically detecting intrinsic evoked response of apatient's heart can be found in Zhu et al., Accelerometer-Based HeartSound Detection for Autocapture,” U.S. Pat. No. 6,650,940, filed Feb. 2,2008.

OVERVIEW

This document discusses systems, devices and methods for improveddetermination of efficacy of cardiac therapy for a patient or subject.An apparatus example can include an implantable therapy circuitconfigured to provide bi-ventricular pacing to a subject, a heart soundsignal sensing circuit configured to produce a sensed heart sound signalthat is representative of at least one heart sound associated withmechanical cardiac activity, a memory circuit configured to store one ormore heart sound templates of cardiac capture, and a comparison circuitconfigured to compare a segment of the sensed heart sound signal to theone or more heart sound templates of cardiac capture to identifyventricles in which cardiac capture was induced by the bi-ventricularpacing and generate an indication of the ventricles in which cardiaccapture was induced according to the comparison and providing theindication to at least one of a user or process.

This overview is intended to provide an overview of subject matter ofthe present patent application. It is not intended to provide anexclusive or exhaustive explanation of the invention. The detaileddescription is included to provide further information about the presentpatent application.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 is an illustration of portions of a system that uses anambulatory medical device that is an IMD.

FIG. 2 is an illustration of portions of another system that uses an IMDto provide a therapy to a patient.

FIG. 3 shows a flow diagram of an example of a method of determiningeffective cardiac pacing therapy.

FIG. 4 is block diagram of portions of an example of an ambulatorymedical device that determines the efficacy of cardiac pacing therapyprovided to a subject.

DETAILED DESCRIPTION

An ambulatory medical device may include one or more of the features,structures, methods, or combinations thereof described herein. Forexample, an ambulatory cardiac monitor or cardiac stimulator may beimplemented to include one or more of the advantageous features orprocesses described below. It is intended that such a monitor,stimulator, or other implantable, partially implantable, or wearabledevice need not include all of the features described herein, but may beimplemented to include selected features that provide for uniquestructures or functionality. Such a device may be implemented to providea variety of therapeutic or diagnostic functions.

FIG. 1 is an illustration of portions of a system that uses anambulatory medical device that is an IMD 110. Examples of IMD 110include, without limitation, a pacer, a defibrillator, a cardiacresynchronization therapy (CRT) device, or a combination of suchdevices. The system 100 also typically includes an IMD programmer orother external device 170 that communicates wireless signals 190 withthe IMD 110, such as by using radio frequency (RF) or other telemetrysignals. The external device 170 may communicate with a remote systemvia a network, such as a computer network or cellular phone network. Insome examples, the remote system provides patient management functionsand may include one or more servers to perform the functions.

The IMD 110 is shown coupled by one or more leads 108A-C to heart 105.Cardiac leads 108A-C include a proximal end that is coupled to IMD 110and a distal end, coupled by electrical contacts or “electrodes” to oneor more portions of a heart 105. The electrodes typically delivercardioversion, defibrillation, pacing, or resynchronization therapy, orcombinations thereof to at least one chamber of the heart 105. Theelectrodes may be electrically coupled to sense amplifiers to senseelectrical cardiac signals.

Heart 105 includes a right atrium 100A, a left atrium 100B, a rightventricle 105A, a left ventricle 105B, and a coronary sinus 120extending from right atrium 100A. Right atrial (RA) lead 108A includeselectrodes (electrical contacts, such as ring electrode 125 and tipelectrode 130) disposed in an atrium 100A of heart 105 for sensingsignals, or delivering pacing therapy, or both, to the atrium 100A.

Right ventricular (RV) lead 108B includes one or more electrodes, suchas tip electrode 135 and ring electrode 140, for sensing signals,delivering pacing therapy, or both sensing signals and delivering pacingtherapy. Lead 108B optionally also includes additional electrodes, suchas for delivering atrial cardioversion, atrial defibrillation,ventricular cardioversion, ventricular defibrillation, or combinationsthereof to heart 105. Such electrodes typically have larger surfaceareas than pacing electrodes in order to handle the larger energiesinvolved in defibrillation. Lead 108B optionally providesresynchronization therapy to the heart 105. Resynchronization therapy istypically delivered to the ventricles in order to better synchronize thetiming of depolarizations between ventricles.

The IMD 110 may include a third cardiac lead 108C attached to the IMD110 through the header 155. The third cardiac lead 108C includeselectrodes 160 and 165 placed in a coronary vein lying epicardially onthe left ventricle (LV) 105B via the coronary vein. The third cardiaclead 108C may include a ring electrode 185 positioned near the coronarysinus (CS) 120. Although only two electrodes are shown in the example ofthe Figure, lead 108C may include three electrodes, four electrodes, orany number of electrodes as desired.

Lead 108B may include a first defibrillation coil electrode 175 locatedproximal to tip and ring electrodes 135, 140 for placement in a rightventricle, and a second defibrillation coil electrode 180 locatedproximal to the first defibrillation coil 175, tip electrode 135, andring electrode 140 for placement in the superior vena cava (SVC). Insome examples, high-energy shock therapy is delivered from the first orRV coil 175 to the second or SVC coil 180. In some examples, the SVCcoil 180 is electrically tied to an electrode formed on thehermetically-sealed IMD housing or can 150. This improves defibrillationby delivering current from the RV coil 175 more uniformly over theventricular myocardium. In some examples, the therapy is delivered fromthe RV coil 175 only to the electrode formed on the IMB can 150. In someexamples, the coil electrodes 175, 180 are used in combination withother electrodes for sensing signals.

Note that although a specific arrangement of leads and electrodes areshown in the illustration, the present methods and systems will work ina variety of configurations and with a variety of electrodes. An IMB maybe configured with a variety of electrode arrangements, includingtransvenous, endocardial, and epicardial electrodes (i.e., intrathoracicelectrodes), and/or subcutaneous, non-intrathoracic electrodes,including can, header, and indifferent electrodes, and subcutaneousarray or lead electrodes (i.e., non-intrathoracic electrodes).

The IMD 110 can also include a heart signal sensing circuit 111. Theheart sound signal sensing circuit 111 may be configured to produce asensed heart sound signal that is representative of at least one heartsound associated with mechanical cardiac activity of a subject. Someexamples of a heart sound signal sensing circuit 111 can include anaccelerometer, a microphone, or other suitable heart sound sensor.

FIG. 2 is an illustration of portions of another system 200 that uses anIMD 210 to provide a therapy to a patient 202. The system 200 typicallyincludes an external device 270 that communicates with a remote system296 via a network 294. The network 294 can be a communication networksuch as a phone network or a computer network (e.g., the internet). Insome examples, the external device 270 includes a repeater andcommunicates via the network using a link 292 that may be wired orwireless. In some examples, the remote system 296 provides patientmanagement functions and may include one or more servers 298 to performthe functions.

The IMB may track what therapy was provided to a patient or subjectaccording to whether the device delivered a pacing pulse to a particularheart chamber of the subject. For example, counters may be used by thedevice to track bi-ventricular or bi-V pacing stimulation pulsesprovided. However, in some situations, device-based counters mayinaccurately estimate the degree of bi-V pacing that effectivelycaptures the heart. This can be especially true if the device isestimating effective pacing therapy during an episode of atrialfibrillation (AF) experienced by the subject. The actual degree of bi-Vpacing that is effective may be lower than an estimate of bi-V pacingdelivered determined using device counters. Also, a fusion beat canoccur when a device delivers a pacing pulse to a ventricle, but themajority of the ventricle is still activated through intrinsicdepolarization. The occurrence of fusion beats can impact the accuracyof the estimate of effective bi-V pacing when using device counters.

Heart sounds are associated with mechanical cardiac activity. This is incontrast to electrical cardiac activity that is associated withelectrical action potentials due to cardiac depolarization. A “heartsound” can include a first heart sound (S1), a second heart sound (S2),a third heart sound (S3), a fourth heart sound (S4), or any componentsthereof, such as the aortic component of S2 (A2), the pulmonarycomponent of S2 (P2), or other broadband sounds or vibrations associatedwith mechanical activity of the heart, such as valve closures or fluidmovement (e.g., a heart murmur, etc.). Heart sounds can also include oneor more broadband chest sounds, such as may result from one or more ofmitral regurgitation, left ventricle dilation, etc.

Sensing heart sounds can be used to determine if a pacing stimulationpulse induced an evoked response or cardiac capture of the heart. Onlysensing electrical signals may provide an indication of an electricalaction potential traversing a region of the heart as the result of apacing stimulation pulse, but may not provide an indication that theaction potential induced a mechanical contraction. Heart sounds can beused, with or without device counters, to discriminate effective captureof the left ventricle (LV), right ventricle (RV), or both ventriclesfrom no capture or inadequate capture of the ventricles.

FIG. 3 shows a flow diagram of an example of a method 300 of determiningeffective cardiac pacing therapy. At block 305, a bi-ventricular (bi-V)pacing pulse is provided to the subject by an ambulatory medical deviceas part of cardiac pacing therapy (e.g., CRT). In certain examples, theambulatory medical device is an implantable medical device. The bi-Vpacing pulse includes an electrical pacing stimulation pulse deliveredto the RV and an electrical stimulation pulse delivered to the LV.

At block 310, a heart sound signal is sensed by the device inassociation with providing the bi-V pacing pulse. Characteristics orattributes of the sensed heart sound signal can indicate whether or notcapture occurred in one or both of the ventricles. One method fordevice-based identification of capture in heart sound signals is usingtemplate comparisons. A template can represent a segment of a sensedheart sound signal. In some examples, multiple heart sound signals aresensed and a central tendency (e.g., an average) of the heart soundsignals can be used as the template. Using a central tendency of thesignal can help to remove or reduce noise from the template. The one ormore sensed heart sound signals can be compared to one or more heartsound templates representative of RV capture only, LV capture only, andcapture in both ventricles (bi-V capture), to determine an assessment ofcapture resulting from the pacing stimulation.

At block 315, a segment of the sensed heart sound signal can be comparedto one or more heart sound templates indicative of cardiac capture(e.g., RV capture, LV capture, or bi-V capture). In this way, theventricles can be identified in which capture was induced by the bi-Vpacing pulse. At block 320, an indication of those ventricles in whichcapture was induced can be generated and provided to at least one of auser, physician, or process. Because confirmation of capture isdetermined using the heart sound signal, the method may provide a moreaccurate determination of the degree of bi-V pacing therapy that iseffectively delivered.

FIG. 4 is block diagram of portions of an example of an ambulatorymedical device 400 that determines the efficacy of cardiac pacingtherapy provided to a subject. The device includes an implantabletherapy circuit 405 that provides a bi-V pacing pulse to the subject aspart of cardiac pacing therapy. The cardiac pacing therapy can includeCRT or bradycardia pacing therapy.

The device also includes a heart sound signal sensing circuit 410 and amemory circuit 415. The heart sound signal sensing circuit 410 producesa sensed heart sound signal representative of at least one heart sound.The heart sound is associated with mechanical activity of the heart ofthe subject, as discussed previously. The memory circuit 415 can beconfigured to store one or more heart sound templates that arerepresentative of a heart sound signal sensed during cardiac capture.For example, the memory circuit 415 may be configured to store a RVcapture template, a LV capture template, a bi-V capture template, atemplate of intrinsic an heat beat, and combinations thereof.

The ambulatory medical device 400 may further includes a comparisoncircuit 420 in electrical communication with the heart sound signalsensing circuit 410 and the memory circuit 415. The electricalcommunication allows electrical signals to be communicated between thecomparison circuit 420 and the heart sound signal sensing circuit 410and the memory circuit 415 even though there may be intervening circuitsbetween the comparison circuit 420 and the heart sound signal sensingcircuit 410 and the memory circuit 415. The comparison circuit 420 canbe configured to compare at least a segment of the sensed heart soundsignal to the one or more heart sound templates representative ofcardiac capture. For example, the comparison circuit 420 may beconfigured to calculate a coefficient of correlation for at least one ormore templates based on the comparison. The coefficient of correlationmay provide a metric of how well the sensed signal correlates with thespecific heart sound template. The sensed heart sound signal may bedetermined to be representative of the template when the calculatedcoefficient of correlation exceeds a threshold coefficient value. Insome cases, the threshold coefficient value can be specified orprogrammed by the device manufacturer or a user (e.g., a physician). Insome cases, the sensed heart sound signal may be determined to berepresentative of one of the one or more templates when the calculatedcorrelation coefficient corresponding to the template has the highestvalue among all the calculated correlation coefficients.

The comparison circuit 420 may be included in a control circuit 425. Thecontrol circuit 425 can be a microprocessor, a digital signal processor,application specific integrated circuit (ASIC), microprocessor, or othertype of processor, interpreting or executing instructions in softwaremodules or firmware modules. The control circuit 425 can include othercircuits or sub-circuits to perform the functions described. Thesecircuits may include software, hardware, firmware or any combinationthereof. Multiple functions can be performed in one or more of thecircuits as desired.

The comparison circuit 420 can be configured to compare the segment ofthe sensed heart sound signal to one or more heart sound signaltemplates to identify ventricles in which cardiac capture was induced bythe bi-ventricular pacing pulse. The one or more heart sound signaltemplates may be representative of at least one of a heart sound signalsensed during pacing of only a RV, a heart sound signal sensed duringpacing of only a LV, a heart sound signal sensed during bi-V pacing, ora heart sound signal representative of ventricular contraction resultingfrom intrinsic depolarization. To obtain the heart sound signal segment,the sensing of the heart sound signal can be gated or triggered bydelivery of the pacing pulse. In another example, the segment of thesensed heart sound signal can be identified by algorithmicallydetermining a heart sound (e.g., the S1 heart sound) in the sensed heartsound signal.

In some examples, the comparison circuit 420 can be configured togenerate an indication of the ventricle or ventricles in which capturewas induced according to the comparison, or generates an indication ofno capture according to the comparison. The indication can be providedto a user or a process. In some examples, the device includes one ormore counters. The indication generated by the comparison circuit 420can be used to update one or more of a count of capture induced in theRV only by the bi-V pacing pulse, a count of capture induced in the LVonly, a count of capture induced in both ventricles, and a count of lackof capture induced in the ventricles by the bi-V pace pulse. It shouldbe noted that this is different than merely counting in which heartchamber a pace pule was delivered because effectiveness orineffectiveness of the pace pulse is confirmed using heart sounds.

In certain examples, the heart sound signal sensing circuit 410 senses aheart sound signal that includes at least a portion of a sensed S1 heartsound. The comparison circuit 420 compares a segment of the sensed heartsound signal that includes at least the portion of the S1 heart sound toone or more templates representative of an S1 heart sound. The S1templates can be representative of one or both of capture andnon-capture, and the indication can be generated by the comparisoncircuit 420 according to the result of the comparison. Using acomparison of the S1 heart sound to templates representative of RVcapture only, LV capture only, bi-V capture, and intrinsic cardiacdepolarization can provide an indication of capture of the ventricles.

In some examples, the device includes a cardiac signal sensing circuit430 and a detection circuit 435. The cardiac signal sensing circuit 430can be configured to provide a sensed cardiac signal representative ofelectrical cardiac activity of the subject. Some examples of a cardiacsignal sensing circuit are a sense amplifier in electrical communicationwith implantable electrodes or with surface electrodes. The cardiacsignal may be sensed as an electrogram or an electrocardiogram. Thedetection circuit 435 can be configured to detect an episode of AF usingthe sensed cardiac signal. In certain examples, the detection circuit435 can include a heart rate detection circuit and detects AF using adetected atrial depolarization rate. The control circuit 425 caninitiate delivery of one or more bi-V pacing pulses during the detectedepisode of AF. The comparison circuit 420 may generate an indication ofthe ventricles in which capture was induced by one or more bi-V pacingpulses provided during the detected episode of AF. The device mayinclude separate counters to specifically track counts for eventsdetected during AF.

In some examples, the comparison circuit 420 can be configured to scalea heart sound template in as a function of detected heart rate. Theheart sound templates representative of cardiac capture can be scaled inone or both of time and amplitude. For instance, a heart sound templatecould be scaled in one or both of amplitude (e.g., by shrinking orexpanding the template signal along the y-axis) and time (e.g.,shrinking or expanding the template signal along x-axis) as a functionof heart rate. At a higher high rate, it may be expected for the S1heart sound to be louder (therefore the amplitude of the signal may bescaled up) and also since the cardiac cycle is shortened when the rateis higher, the duration of S1 may be shorter (therefore the templatesignal may be scaled shorter in time). Hence, the comparison circuit 420may scale the heart sound template used in the comparison according tothe sensed heart rate.

The device 400 may generate its own templates for use by the comparisoncircuit 420 in the comparisons. According to some examples, the deviceincludes a template circuit 440. The template circuit 440 may generateheart sound templates representative of cardiac capture in the RV, inthe LV, in both ventricles, and heart sound templates representative ofventricular contraction resulting from an intrinsic depolarization.

In some examples, the control circuit 425 can be configured to initiatea template mode to generate a heart sound template. In the templatemode, one or more electrical stimulation pulses are delivered to one orboth ventricles according to the kind of template of interest (e.g., RVonly, LV only, bi-V), or delivery of pacing pulses can be suspended ifthe template of interest is for intrinsic heart beats. The electricalstimulation pulses may be provided using a stimulation interval that isless than a shortest detected intrinsic depolarization interval and mayhave a high enough amplitude to ensure capture by the pulses. In certainexamples, the shortest interval detected over a specified number ofprevious cardiac cycles is used as the shortest interval. Pacing at aninterval that is less than a shortest intrinsic interval is useful toavoid the presence of intrinsic fusion beats in the heart sound signalor signals used to generate a heart sound template. In this way,separate templates can be constructed for true RV only heart beats, trueLV only heart beats, and true bi-V heart beats. A separate template canalso be generated for true intrinsic beats by suspending pacingaltogether for a specified number of intrinsic beats. Once heart soundtemplates are formed, the device can chronically monitor heart beats andcompare the heat sound features to the templates to correctly classifyheartbeats based on a calculated similarity to, or difference from, thefour types of heart sound templates.

In some examples, the control circuit 425 can be configured to initiatethe generation of heart sound templates in a confirmation mode. Inconfirmation mode, the template circuit 440 generates a candidate heartsound template representative of cardiac capture in the RV only, cardiaccapture in the LV only, or cardiac capture in both ventricles usingheart sound signals sensed during pacing of the RV only, the LV only, orboth ventricles, respectively. The template circuit 440 may alsogenerate a candidate heart sound template corresponding to ventricularcontraction resulting from intrinsic depolarization. When a candidatetemplate is obtained, the control circuit 425 may cause the template tobe communicated to a second device (e.g., by inductive or radiofrequency telemetry) for presentation (e.g., display) to a user. Afterinspecting the candidate template, the user may enter an indication ofacceptance of the candidate template for use in detecting cardiaccapture, such as by entering the indication into the second device via auser interface for example. The second device may then communicate theindication to the control circuit 425.

Upon receiving the indication of acceptance of the candidate heart soundtemplate, the control circuit may classify the candidate heart soundtemplate as usable in a comparison to segment of a sensed heart soundsignal. The classification may include storing the candidate template ina different area of memory reserved for templates that have beenaccepted by a user, or may include setting a flag or other indicatorthat the candidate template has been accepted by a user. The controlcircuit 425 may then initiate a comparison of a segment of a sensedheart sound signal to the candidate template as a result of one or bothof the received indication of acceptance and the re-classification ofthe candidate template. If the template is not accepted, it may bediscarded.

In some examples, the control circuit 425 can be configured to initiatethe generation of heart sound templates in an automatic mode. Inautomatic mode, similar to the confirmation mode, the template circuit440 generates a candidate heart sound template representative of cardiaccapture in the RV only, cardiac capture in the LV only, or cardiaccapture in both ventricles using heart sound signals sensed duringpacing of the RV only, the LV only, or both ventricles, respectively.

When a candidate template is generated, the template circuit calculatesa metric of separation of the candidate heart sound template from aheart sound template representative of ventricular contraction resultingfrom intrinsic depolarization. The heart sound template associated withintrinsic depolarization may also have been generated by the templatecircuit 440 by suspending pacing stimulation for a specified number ofcardiac cycles. Based on the calculated metric, the control circuit 425may classify the candidate heart sound template as usable in asubsequent comparison to a segment of a sensed heart sound signal, orthe candidate template may be discarded.

The control circuit 425 may compare the calculated metric to a metricthreshold value, and classify the candidate heart sound template asusable when the calculated metric satisfies the threshold. Theclassification of the template as usable may include storing thecandidate template in a different area of memory reserved for templatesthat have been accepted by a user, or may include setting a flag orother indicator that the candidate template has been accepted by a user.The control circuit 425 may then initiate a comparison of a segment of asensed heart sound signal to the candidate template that has beenclassified as usable. The process may be repeated multiple times by thedevice and templates with heart sound features having the greatestdegree of separation from the intrinsic heart sound features can beselected as templates for a given mode of pacing.

While the description has focused on bi-V pacing, the methods, devices,and systems described herein can also be applied to other types ofpacing such as RV only or LV only to verify capture. For instance, inpacemakers ventricular pacing pulses are typically provided to the RVonly and the methods described can be used to distinguish between RVonly capture and loss of capture or intrinsic depolarization.

Using heart sounds to determine efficacy of pacing adds a mechanicalassessment of the response of the heart to electrical pacing therapy.Knowing the efficacy of the device-based pacing therapy prescribed mayassist a physician in optimizing the performance of the device for aspecific patient or subject. If the percentage of capture is presentedto a physician, this measure can be used to reprogram (e.g., optimize)parameters for CRT. This reprogramming or re-optimizing may includechanging the AV delay, the VV delay, a pacing site, and stimulationparameters (e.g., pacing amplitude, pulse width, etc.). The process ofre-optimization of parameters may be triggered when the percentage ofcapture drops below a threshold in order to increase or maximize theefficacy of pacing therapy.

ADDITIONAL NOTES

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown or described. However, the present inventors alsocontemplate examples in which only those elements shown or described areprovided. Moreover, the present inventors also contemplate examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

In the event of inconsistent usages between this document and anydocuments so incorporated by reference, the usage in this documentcontrols.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In this document, the terms “including” and “inwhich” are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, composition, formulation, or process that includes elements inaddition to those listed after such a term in a claim are still deemedto fall within the scope of that claim. Moreover, in the followingclaims, the terms “first,” “second,” and “third,” etc. are used merelyas labels, and are not intended to impose numerical requirements ontheir objects.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, in an example, the code can be tangiblystored on one or more volatile, non-transitory, or non-volatile tangiblecomputer-readable media, such as during execution or at other times.Examples of these tangible computer-readable media can include, but arenot limited to, hard disks, removable magnetic disks, removable opticaldisks (e.g., compact disks and digital video disks), magnetic cassettes,memory cards or sticks, random access memories (RAMs), read onlymemories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription as examples or embodiments, with each claim standing on itsown as a separate embodiment, and it is contemplated that suchembodiments can be combined with each other in various combinations orpermutations. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

The claimed invention is:
 1. An apparatus comprising an implantable therapy circuit configured to provide cardiac pacing therapy; a heart sound signal sensing circuit configured to produce a sensed heart sound signal that is representative of at least one heart sound associated with mechanical cardiac activity of a subject; a memory circuit configured to store one or more heart sound templates of cardiac capture; and a control circuit configured to identify cardiac capture by the cardiac pacing therapy using the sensed heart sound signal and a heart sound template of cardiac capture.
 2. The apparatus of claim 1, wherein the comparison circuit is configured to comp are a segment of the sensed heart sound signal includes comparing the segment of the sensed heart sound signal to at least one of a template heart sound signal representative of a heart sound signal sensed during pacing of only a right ventricle (RV), a template heart sound signal representative of a heart sound signal sensed during pacing of only a left ventricle (LV), and a template heart sound signal representative of a heart sound signal sensed during bi-ventricular pacing.
 3. The apparatus of claim 1, including: a cardiac signal sensing circuit configured to provide a sensed cardiac signal representative of electrical cardiac activity of the subject; a detection circuit configured to detect an episode of atrial fibrillation using the sensed cardiac signal; and a control circuit configured to initiate delivery of one or more pacing pulses during the detected episode of atrial fibrillation, wherein the comparison circuit is configured to generate an indication of the ventricles in which capture was induced by one or more pacing pulses provided during the detected episode of atrial fibrillation.
 4. The apparatus of claim 3, wherein the control circuit is configured to initiate delivery of one or more bi-ventricular pacing pulses during the detected episode of atrial fibrillation, and the comparison circuit is configured to generate the indication of the ventricles in which capture was induced by one or more bi-ventricular pacing pulses provided during the detected episode of atrial fibrillation.
 5. The apparatus of claim 1, wherein the heart sound signal sensing circuit is configured to sense a heart sound signal that includes at least a portion of a sensed S1 heart sound, and wherein the comparison circuit is configured to comp are a segment of the sensed heart sound signal that includes the at least a portion of a sensed S1 heart sound to one or more templates representative of an S1 heart sound.
 6. The apparatus of claim 1, wherein the comparison circuit is configured to generate an indication that up dates, according to the comparison, a count of capture induced in the RV only, a count of capture induced in the LV only, a count of capture induced in both ventricles, and a count of lack of capture in the ventricles.
 7. The apparatus of claim 1, including a template circuit configured to generate heart sound templates representative of cardiac capture in the RV, in the LV, and in both ventricles, and generating a heart sound template representative of ventricular contraction due to intrinsic depolarization.
 8. The apparatus of claim 6, including a control circuit configured to initiate a template mode in which one or more electrical stimulation pulses are delivered to one or both ventricles, wherein the electrical stimulation pulses are provided using a stimulation interval that is less than a shortest detected intrinsic depolarization interval, and wherein the template circuit is configured to generate a heart sound template using one or more heart sound signals sensed when providing the one or more electrical stimulation pulses to the one or both ventricles in the template mode.
 9. The apparatus of claim 1, including: a template circuit configured to: generate a candidate heart sound temp late representative of cardiac capture resulting from an electrical stimulation pulse delivered to at least one of the RV only, the LV only, or to both ventricles; and calculate a metric of separation of the candidate heart sound template from a heart sound temp late representative of ventricular contraction resulting from intrinsic depolarization; and a control circuit configured to initiate a comparison of a segment of a sensed heart sound signal to the candidate heart sound template according to the calculated metric.
 10. The apparatus of claim 1, including a heart rate detection circuit, wherein the comparison circuit is configured to scale the one or more heart sound templates of cardiac capture in one or both of time and amplitude as a function of detected heart rate, wherein comp are the segment of the sensed heart sound signal to one or more scaled heart sound templates.
 11. The apparatus of claim 1, wherein the implantable therapy circuit is further configured to provide a bi-ventricular pacing pulse to a subject as part of the cardiac pacing therapy, wherein the bi-ventricular pacing pulse includes providing an electrical stimulation pulse to a right ventricle and an electrical stimulation pulse to a left ventricle; and wherein the control circuit includes a comparison circuit configured to: compare a segment of the sensed heart sound signal to at least one of a template heart sound signal representative of capture of only a first location of the subject's heart, a template heart sound signal representative of capture of only a second location of the subject's heart, and a template heart sound signal representative of capture of both the first and second locations of the subject's heart; identify ventricles in which cardiac capture was induced by a pacing pulse; and generate an indication of the ventricles in which capture was induced or an indication of no cardiac capture of a ventricle according to the comparison and providing the indication to at least one of a user or process.
 12. A method comprising providing, to a subject by an implantable device, a cardiac pacing therapy; sensing a heart sound signal from the subject in association with the bi-ventricular pacing pulse, wherein a heart sound signal is associated with mechanical activity of a subject's heart; and identifying cardiac capture by the cardiac pacing therapy using the sensed heart sound signal and a template heart sound signal representative of cardiac capture.
 13. The method of claim 12, further including: providing a bi-ventricular pacing pulse as p art of the cardiac pacing therapy, wherein the bi-ventricular pacing pulse includes providing an electrical stimulation pulse to a right ventricle and an electrical stimulation pulse to a left ventricle; comparing by the implantable device, a segment of the sensed heart sound signal to at least one of a template heart sound signal representative of capture only at a first location of the heart of the subject, a template heart sound signal representative of capture only at a second location of the heart of the subject, and a template heart sound signal representative of capture at both of the first and second locations of the heart of the subject; identifying ventricles in which cardiac capture was induced by a pacing pulse; and generating an indication of the ventricles in which capture was induced or an indication of no cardiac capture of a ventricle according to the comparison and providing the indication to at least one of a user or process.
 14. The method of claim 12, wherein comparing a segment of the sensed heart sound signal includes comparing the segment of the sensed heart sound signal to at least one of a template heart sound signal representative of a heart sound signal sensed during pacing of only a right ventricle (RV), a template heart sound signal representative of a heart sound signal sensed during pacing of only a left ventricle (LV), and a template heart sound signal representative of a heart sound signal sensed during bi-ventricular pacing.
 15. The method of claim 12, including detecting, by the implantable device, an episode of atrial fibrillation (AF), wherein providing a pacing pulse includes providing one or more pacing pulses during the episode of AF, and wherein the generating an indication includes generating an indication of the ventricles in which capture was induced by the one or more pacing pulses provided during the episode of atrial fibrillation.
 16. The method of claim 15, wherein providing a pacing pulse includes providing one or more bi-ventricular pacing pulses during the episode of AF.
 17. The method of claim 12, including: determining a heart rate of the subject; and scaling the one or more heart sound templates of cardiac capture in or both of time and amplitude as a function of the determined heart rate, wherein comparing a segment of the sensed heart sound signal includes comparing a segment of the sensed heart sound signal to one or more scaled heart sound templates.
 18. The method of claim 12, wherein sensing a heart sound signal includes sensing a heart sound signal that includes at least a portion of a sensed S1 heart sound, and wherein comparing a segment of the sensed heart sound signal includes comparing a segment of the sensed heart sound signal that includes the at least a portion of a sensed S1 heart sound to one or more templates representative of an S1 heart sound, and wherein generating an indication includes updating according to the comparison, a count of capture induced in the RV only, a count of capture induced in the LV only, a count of capture induced in both ventricles, and a count of lack of capture in the ventricles.
 19. The method of claim 12, including generating, by the implantable device, heart sound templates representative of cardiac capture in the RV, in the LV, and in both ventricles, and generating a heart sound template representative of ventricular contraction due to intrinsic depolarization, wherein generating heart sound templates representative of cardiac capture includes generating a heart sound template using one or more heart sound signals sensed when providing electrical stimulation pulses to one or both ventricles using a stimulation interval that is less than a shortest detected intrinsic depolarization interval.
 20. The method of claim 12, including: generating, by the implantable device, a candidate heart sound template representative of at least one of cardiac capture in the RV only, cardiac capture in the LV only, cardiac capture in both ventricles, or ventricular contraction resulting from intrinsic depolarization; receiving, by the implantable device, an indication of acceptance of the candidate heart sound template; and classifying the candidate heart sound template as usable in a comparison to a segment of a sensed heart sound signal up on receiving the indication of acceptance of the candidate template. 